The following generally relates to determining a travel curve for circuit breaker interrupter contacts of a high-voltage circuit breaker and more particularly to estimating one or more travel curves with or without actual contact travel distance measurements being made during an open and/or closed breaker operation via contact travel sensors.
Condition-based maintenance of high-voltage circuit breakers has been implemented by incorporating microprocessor controlled on-line condition monitoring devices and sensors with the high-voltage circuit breakers. Generally, the sensors/devices are configured to measure information used to calculate critical parameters that represent the health of the circuit breaker. An example of such a sensor is a contact travel sensor. Such a sensor is capable of tracking the position of the breaker contacts as they move from open to closed positions, and vice versa, with a resolution of about 0.1-1.0 mm (millimeters) and a sample period of typically 0.1-0.3 ms (milliseconds).
The graphical representation of the contact position over time has been referred to as the travel curve. A travel curve is recorded over an acquisition time period, for example, of 150 ms or so. The types and sequences of operation that are captured during this time period are close (C), open (O), and close/open (C-O). The open operation has been referred to as a “trip” operation. More complex sequences such as open/close/open (O-C-O) may be captured with longer acquisition time periods or captured over two ore more discontinuous time periods.
Once a travel curve is recorded, important parameters can be derived from it. These parameters include, but are not limited to: over travel, which is the distance temporarily traveled in excess of the designed end-position; rebound, which is the distance temporarily traveled away from the designed end-position as result of over travel; total travel, which is the distance traveled between the point farthest from the end-position and the point farthest from the start-position; reaction time, which is the time from initiation of the operation until the contacts start to move; contact velocity, which is the slope of a straight line connecting two points on the travel curve as specified by the manufacturer, and mechanism time, which is the time from initiation of the operation until a contact position is reached where the contacts engage or separate.
The component of a circuit breaker designed to make or break currents of various magnitudes is called the interrupter. During the service life of the circuit breaker, its interrupter is subjected to wear. The wear is accumulated during arcing periods, i.e. the period during an open or close operation where the contacts are physically separated by a gap and the gap is bridged by an electrical arc. The arc bridges a dedicated set of contacts that are designed for this purpose and are referred to as arcing contacts. Various methods exist to calculate or at least approximate interrupter wear by measuring the current through the circuit breaker. These methods are sometimes referred to as interrupter wear algorithms.
In addition to the breaker current, an interrupter wear algorithm must have knowledge of the point in time when the arcing contacts separate during an open operation or engage during a close operation. This knowledge may come from monitoring an auxiliary switch that is mechanically linked to the breaker contacts and closes and opens at the same time the arcing contacts separate or engage. Examples of such auxiliary switches include, but are not limited to, A and B switches. An A switch closes during a close operation after contacts have traveled about 70% towards their end-position, and a B-switch opens during a close operation after the contacts have traveled about 30% towards their end-position. The exact values are breaker and model dependent. The A-switch opens and the B-switch closes during an open operation. The typical use of auxiliary switches is for control schemes and for remote indication of the breaker contacts. Because the latter function is fundamental to the operation of high-voltage circuit breakers, breakers are equipped with auxiliary switches as standards components.
Besides interrupter wear calculation, typical on-line condition monitoring devices use auxiliary switches to monitor the breaker timing. However, rather than deriving parameters such as reaction time or contact velocity, they simply monitor whether the auxiliary switches close or open within a specified time range. Alternatively, if a travel sensor is used, the time when the arcing contacts engage or separate can by derived by finding the corresponding point on the travel curve. Use of a travel sensor also enables more sophisticated interrupter wear algorithms. Not only can the time be determined when the arcing contact engage or separate but also when other parts of interrupter such as nozzles are subjected to arcing as this is a function of the contact position.
Travel measurement is not only employed by on-line condition monitors. It is also used as part of off-line measurements during factory tests, commissions and yearly (or other time-based) maintenance. Because its use is ubiquitous in the electric power industry, the graphical representation in form of a travel curve itself has value to the user in addition to the important parameters that can be derived from the travel curve.
Unfortunately, the use of travel sensors for on-line condition monitoring poses various technical and economical challenges. While various rotary and linear position encoders are commercially available, their successful installation on a high-voltage circuit breaker is non-trivial. That is, the mounting locations that are used for off-line travel sensors can generally not be used, because these locations are not weather protected. The locations that are weather protected often don't have parts of the mechanism accessible that are suitable to pick up either linear or rotary motion, in particular motion which is proportional to or at least unambiguously linked to the contact travel to be measured.
Once a suitable mounting location for an on-line travel sensor is identified and the necessary mounting provisions engineered, the travel sensor arrangement should be life-tested for at least 2000 operations (C and O) to ensure that the mounting and/or the sensor will not fail during its intended service life. Life testing of a travel sensor installation is economical only during the prototyping phase of a new circuit breaker model, since life test have to be performed either way. In addition, it is more costly for current production models because a breaker has to be built specifically for the purpose of the travel sensor life test and can obviously not be sold afterwards. Furthermore, for models that are out of production, the only specimens are breakers still in service and subjecting these breakers to a life test is not a viable option. Therefore, designing an on-line monitoring system that uses travel sensors is either not economically viable or carries great product liability risks.